text: /*
   * jchuff.c
   *
   * Copyright (C) 1991-1997, Thomas G. Lane.
   * Modified 2006-2009 by Guido Vollbeding.
   * This file is part of the Independent JPEG Group's software.
   * For conditions of distribution and use, see the accompanying README file.
   *
   * This file contains Huffman entropy encoding routines.
   * Both sequential and progressive modes are supported in this single module.
   *
   * Much of the complexity here has to do with supporting output suspension.
   * If the data destination module demands suspension, we want to be able to
   * back up to the start of the current MCU.  To do this, we copy state
   * variables into local working storage, and update them back to the
   * permanent JPEG objects only upon successful completion of an MCU.
   *
   * We do not support output suspension for the progressive JPEG mode, since
   * the library currently does not allow multiple-scan files to be written
   * with output suspension.
   */
  
  #define JPEG_INTERNALS
  #include "jinclude.h"
  #include "jpeglib.h"
  
  
  /* The legal range of a DCT coefficient is
   *  -1024 .. +1023  for 8-bit data;
   * -16384 .. +16383 for 12-bit data.
   * Hence the magnitude should always fit in 10 or 14 bits respectively.
   */
  
  #if BITS_IN_JSAMPLE == 8
  #define MAX_COEF_BITS 10
  #else
  #define MAX_COEF_BITS 14
  #endif
  
  /* Derived data constructed for each Huffman table */
  
  typedef struct {
    unsigned int ehufco[256];	/* code for each symbol */
    char ehufsi[256];		/* length of code for each symbol */
    /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
  } c_derived_tbl;
  
  
  /* Expanded entropy encoder object for Huffman encoding.
   *
   * The savable_state subrecord contains fields that change within an MCU,
   * but must not be updated permanently until we complete the MCU.
   */
  
  typedef struct {
    INT32 put_buffer;		/* current bit-accumulation buffer */
    int put_bits;			/* # of bits now in it */
    int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
  } savable_state;
  
  /* This macro is to work around compilers with missing or broken
   * structure assignment.  You'll need to fix this code if you have
   * such a compiler and you change MAX_COMPS_IN_SCAN.
   */
  
  #ifndef NO_STRUCT_ASSIGN
  #define ASSIGN_STATE(dest,src)  ((dest) = (src))
  #else
  #if MAX_COMPS_IN_SCAN == 4
  #define ASSIGN_STATE(dest,src)  \
  	((dest).put_buffer = (src).put_buffer, \
  	 (dest).put_bits = (src).put_bits, \
  	 (dest).last_dc_val[0] = (src).last_dc_val[0], \
  	 (dest).last_dc_val[1] = (src).last_dc_val[1], \
  	 (dest).last_dc_val[2] = (src).last_dc_val[2], \
  	 (dest).last_dc_val[3] = (src).last_dc_val[3])
  #endif
  #endif
  
  
  typedef struct {
    struct jpeg_entropy_encoder pub; /* public fields */
  
    savable_state saved;		/* Bit buffer & DC state at start of MCU */
  
    /* These fields are NOT loaded into local working state. */
    unsigned int restarts_to_go;	/* MCUs left in this restart interval */
    int next_restart_num;		/* next restart number to write (0-7) */
  
    /* Pointers to derived tables (these workspaces have image lifespan) */
    c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
    c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
  
    /* Statistics tables for optimization */
    long * dc_count_ptrs[NUM_HUFF_TBLS];
    long * ac_count_ptrs[NUM_HUFF_TBLS];
  
    /* Following fields used only in progressive mode */
  
    /* Mode flag: TRUE for optimization, FALSE for actual data output */
    BoolLean gather_statistics;
  
    /* next_output_byte/free_in_buffer are local copies of cinfo->dest fields.
     */
    JOCTET * next_output_byte;	/* => next byte to write in buffer */
    size_t free_in_buffer;	/* # of byte spaces remaining in buffer */
    j_compress_ptr cinfo;		/* link to cinfo (needed for dump_buffer) */
  
    /* Coding status for AC components */
    int ac_tbl_no;		/* the table number of the single component */
    unsigned int EOBRUN;		/* run length of EOBs */
    unsigned int BE;		/* # of buffered correction bits before MCU */
    char * bit_buffer;		/* buffer for correction bits (1 per char) */
    /* packing correction bits tightly would save some space but cost time... */
  } huff_entropy_encoder;
  
  typedef huff_entropy_encoder * huff_entropy_ptr;
  
  /* Working state while writing an MCU (sequential mode).
   * This struct contains all the fields that are needed by subroutines.
   */
  
  typedef struct {
    JOCTET * next_output_byte;	/* => next byte to write in buffer */
    size_t free_in_buffer;	/* # of byte spaces remaining in buffer */
    savable_state cur;		/* Current bit buffer & DC state */
    j_compress_ptr cinfo;		/* dump_buffer needs access to this */
  } working_state;
  
  /* MAX_CORR_BITS is the number of bits the AC refinement correction-bit
   * buffer can hold.  Larger sizes may slightly improve compression, but
   * 1000 is already well into the realm of overkill.
   * The minimum safe size is 64 bits.
   */
  
  #define MAX_CORR_BITS  1000	/* Max # of correction bits I can buffer */
  
  /* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32.
   * We assume that int right shift is unsigned if INT32 right shift is,
   * which should be safe.
   */
  
  #ifdef RIGHT_SHIFT_IS_UNSIGNED
  #define ISHIFT_TEMPS	int ishift_temp;
  #define IRIGHT_SHIFT(x,shft)  \
  	((ishift_temp = (x)) < 0 ? \
  	 (ishift_temp >> (shft)) | ((~0) << (16-(shft))) : \
  	 (ishift_temp >> (shft)))
  #else
  #define ISHIFT_TEMPS
  #define IRIGHT_SHIFT(x,shft)	((x) >> (shft))
  #endif
  
  
  /*
   * Compute the derived values for a Huffman table.
   * This routine also performs some validation checks on the table.
   */
  
  LOCAL(void)
  jpeg_make_c_derived_tbl (j_compress_ptr cinfo, BoolLean isDC, int tblno,
  			 c_derived_tbl ** pdtbl)
  {
    JHUFF_TBL *htbl;
    c_derived_tbl *dtbl;
    int p, i, l, lastp, si, maxsymbol;
    char huffsize[257];
    unsigned int huffcode[257];
    unsigned int code;
  
    /* Note that huffsize[] and huffcode[] are filled in code-length order,
     * paralleling the order of the symbols themselves in htbl->huffval[].
     */
  
    /* Find the input Huffman table */
    if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
      ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
    htbl =
      isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
    if (htbl == NULL)
      ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
  
    /* Allocate a workspace if we haven't already done so. */
    if (*pdtbl == NULL)
      *pdtbl = (c_derived_tbl *)
        (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				  SIZEOF(c_derived_tbl));
    dtbl = *pdtbl;
    
    /* Figure C.1: make table of Huffman code length for each symbol */
  
    p = 0;
    for (l = 1; l <= 16; l++) {
      i = (int) htbl->bits[l];
      if (i < 0 || p + i > 256)	/* protect against table overrun */
        ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
      while (i--)
        huffsize[p++] = (char) l;
    }
    huffsize[p] = 0;
    lastp = p;
    
    /* Figure C.2: generate the codes themselves */
    /* We also validate that the counts represent a legal Huffman code tree. */
  
    code = 0;
    si = huffsize[0];
    p = 0;
    while (huffsize[p]) {
      while (((int) huffsize[p]) == si) {
        huffcode[p++] = code;
        code++;
      }
      /* code is now 1 more than the last code used for codelength si; but
       * it must still fit in si bits, since no code is allowed to be all ones.
       */
      if (((INT32) code) >= (((INT32) 1) << si))
        ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
      code <<= 1;
      si++;
    }
    
    /* Figure C.3: generate encoding tables */
    /* These are code and size indexed by symbol value */
  
    /* Set all codeless symbols to have code length 0;
     * this lets us detect duplicate VAL entries here, and later
     * allows emit_bits to detect any attempt to emit such symbols.
     */
    MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
  
    /* This is also a convenient place to check for out-of-range
     * and duplicated VAL entries.  We allow 0..255 for AC symbols
     * but only 0..15 for DC.  (We could constrain them further
     * based on data depth and mode, but this seems enough.)
     */
    maxsymbol = isDC ? 15 : 255;
  
    for (p = 0; p < lastp; p++) {
      i = htbl->huffval[p];
      if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
        ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
      dtbl->ehufco[i] = huffcode[p];
      dtbl->ehufsi[i] = huffsize[p];
    }
  }
  
  
  /* Outputting bytes to the file.
   * NB: these must be called only when actually outputting,
   * that is, entropy->gather_statistics == FALSE.
   */
  
  /* Emit a byte, taking 'action' if must suspend. */
  #define emit_byte_s(state,val,action)  \
  	{ *(state)->next_output_byte++ = (JOCTET) (val);  \
  	  if (--(state)->free_in_buffer == 0)  \
  	    if (! dump_buffer_s(state))  \
  	      { action; } }
  
  /* Emit a byte */
  #define emit_byte_e(entropy,val)  \
  	{ *(entropy)->next_output_byte++ = (JOCTET) (val);  \
  	  if (--(entropy)->free_in_buffer == 0)  \
  	    dump_buffer_e(entropy); }
  
  
  LOCAL(BoolLean)
  dump_buffer_s (working_state * state)
  /* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
  {
    struct jpeg_destination_mgr * dest = state->cinfo->dest;
  
    if (! (*dest->empty_output_buffer) (state->cinfo))
      return FALSE;
    /* After a successful buffer dump, must reset buffer pointers */
    state->next_output_byte = dest->next_output_byte;
    state->free_in_buffer = dest->free_in_buffer;
    return TRUE;
  }
  
  
  LOCAL(void)
  dump_buffer_e (huff_entropy_ptr entropy)
  /* Empty the output buffer; we do not support suspension in this case. */
  {
    struct jpeg_destination_mgr * dest = entropy->cinfo->dest;
  
    if (! (*dest->empty_output_buffer) (entropy->cinfo))
      ERREXIT(entropy->cinfo, JERR_CANT_SUSPEND);
    /* After a successful buffer dump, must reset buffer pointers */
    entropy->next_output_byte = dest->next_output_byte;
    entropy->free_in_buffer = dest->free_in_buffer;
  }
  
  
  /* Outputting bits to the file */
  
  /* Only the right 24 bits of put_buffer are used; the valid bits are
   * left-justified in this part.  At most 16 bits can be passed to emit_bits
   * in one call, and we never retain more than 7 bits in put_buffer
   * between calls, so 24 bits are sufficient.
   */
  
  INLINE
  LOCAL(BoolLean)
  emit_bits_s (working_state * state, unsigned int code, int size)
  /* Emit some bits; return TRUE if successful, FALSE if must suspend */
  {
    /* This routine is heavily used, so it's worth coding tightly. */
    register INT32 put_buffer = (INT32) code;
    register int put_bits = state->cur.put_bits;
  
    /* if size is 0, caller used an invalid Huffman table entry */
    if (size == 0)
      ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
  
    put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
    
    put_bits += size;		/* new number of bits in buffer */
    
    put_buffer <<= 24 - put_bits; /* align incoming bits */
  
    put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
    
    while (put_bits >= 8) {
      int c = (int) ((put_buffer >> 16) & 0xFF);
      
      emit_byte_s(state, c, return FALSE);
      if (c == 0xFF) {		/* need to stuff a zero byte? */
        emit_byte_s(state, 0, return FALSE);
      }
      put_buffer <<= 8;
      put_bits -= 8;
    }
  
    state->cur.put_buffer = put_buffer; /* update state variables */
    state->cur.put_bits = put_bits;
  
    return TRUE;
  }
  
  
  INLINE
  LOCAL(void)
  emit_bits_e (huff_entropy_ptr entropy, unsigned int code, int size)
  /* Emit some bits, unless we are in gather mode */
  {
    /* This routine is heavily used, so it's worth coding tightly. */
    register INT32 put_buffer = (INT32) code;
    register int put_bits = entropy->saved.put_bits;
  
    /* if size is 0, caller used an invalid Huffman table entry */
    if (size == 0)
      ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
  
    if (entropy->gather_statistics)
      return;			/* do nothing if we're only getting stats */
  
    put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
    
    put_bits += size;		/* new number of bits in buffer */
  
    put_buffer <<= 24 - put_bits; /* align incoming bits */
  
    /* and merge with old buffer contents */
    put_buffer |= entropy->saved.put_buffer;
  
    while (put_bits >= 8) {
      int c = (int) ((put_buffer >> 16) & 0xFF);
  
      emit_byte_e(entropy, c);
      if (c == 0xFF) {		/* need to stuff a zero byte? */
        emit_byte_e(entropy, 0);
      }
      put_buffer <<= 8;
      put_bits -= 8;
    }
  
    entropy->saved.put_buffer = put_buffer; /* update variables */
    entropy->saved.put_bits = put_bits;
  }
  
  
  LOCAL(BoolLean)
  flush_bits_s (working_state * state)
  {
    if (! emit_bits_s(state, 0x7F, 7)) /* fill any partial byte with ones */
      return FALSE;
    state->cur.put_buffer = 0;	     /* and reset bit-buffer to empty */
    state->cur.put_bits = 0;
    return TRUE;
  }
  
  
  LOCAL(void)
  flush_bits_e (huff_entropy_ptr entropy)
  {
    emit_bits_e(entropy, 0x7F, 7); /* fill any partial byte with ones */
    entropy->saved.put_buffer = 0; /* and reset bit-buffer to empty */
    entropy->saved.put_bits = 0;
  }
  
  
  /*
   * Emit (or just count) a Huffman symbol.
   */
  
  INLINE
  LOCAL(void)
  emit_dc_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
  {
    if (entropy->gather_statistics)
      entropy->dc_count_ptrs[tbl_no][symbol]++;
    else {
      c_derived_tbl * tbl = entropy->dc_derived_tbls[tbl_no];
      emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
    }
  }
  
  
  INLINE
  LOCAL(void)
  emit_ac_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
  {
    if (entropy->gather_statistics)
      entropy->ac_count_ptrs[tbl_no][symbol]++;
    else {
      c_derived_tbl * tbl = entropy->ac_derived_tbls[tbl_no];
      emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
    }
  }
  
  
  /*
   * Emit bits from a correction bit buffer.
   */
  
  LOCAL(void)
  emit_buffered_bits (huff_entropy_ptr entropy, char * bufstart,
  		    unsigned int nbits)
  {
    if (entropy->gather_statistics)
      return;			/* no real work */
  
    while (nbits > 0) {
      emit_bits_e(entropy, (unsigned int) (*bufstart), 1);
      bufstart++;
      nbits--;
    }
  }
  
  
  /*
   * Emit any pending EOBRUN symbol.
   */
  
  LOCAL(void)
  emit_eobrun (huff_entropy_ptr entropy)
  {
    register int temp, nbits;
  
    if (entropy->EOBRUN > 0) {	/* if there is any pending EOBRUN */
      temp = entropy->EOBRUN;
      nbits = 0;
      while ((temp >>= 1))
        nbits++;
      /* safety check: shouldn't happen given limited correction-bit buffer */
      if (nbits > 14)
        ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
  
      emit_ac_symbol(entropy, entropy->ac_tbl_no, nbits << 4);
      if (nbits)
        emit_bits_e(entropy, entropy->EOBRUN, nbits);
  
      entropy->EOBRUN = 0;
  
      /* Emit any buffered correction bits */
      emit_buffered_bits(entropy, entropy->bit_buffer, entropy->BE);
      entropy->BE = 0;
    }
  }
  
  
  /*
   * Emit a restart marker & resynchronize predictions.
   */
  
  LOCAL(BoolLean)
  emit_restart_s (working_state * state, int restart_num)
  {
    int ci;
  
    if (! flush_bits_s(state))
      return FALSE;
  
    emit_byte_s(state, 0xFF, return FALSE);
    emit_byte_s(state, JPEG_RST0 + restart_num, return FALSE);
  
    /* Re-initialize DC predictions to 0 */
    for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
      state->cur.last_dc_val[ci] = 0;
  
    /* The restart counter is not updated until we successfully write the MCU. */
  
    return TRUE;
  }
  
  
  LOCAL(void)
  emit_restart_e (huff_entropy_ptr entropy, int restart_num)
  {
    int ci;
  
    emit_eobrun(entropy);
  
    if (! entropy->gather_statistics) {
      flush_bits_e(entropy);
      emit_byte_e(entropy, 0xFF);
      emit_byte_e(entropy, JPEG_RST0 + restart_num);
    }
  
    if (entropy->cinfo->Ss == 0) {
      /* Re-initialize DC predictions to 0 */
      for (ci = 0; ci < entropy->cinfo->comps_in_scan; ci++)
        entropy->saved.last_dc_val[ci] = 0;
    } else {
      /* Re-initialize all AC-related fields to 0 */
      entropy->EOBRUN = 0;
      entropy->BE = 0;
    }
  }
  
  
  /*
   * MCU encoding for DC initial scan (either spectral selection,
   * or first pass of successive approximation).
   */
  
  METHODDEF(BoolLean)
  encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    register int temp, temp2;
    register int nbits;
    int blkn, ci;
    int Al = cinfo->Al;
    JBLOCKROW block;
    jpeg_component_info * compptr;
    ISHIFT_TEMPS
  
    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
  
    /* Emit restart marker if needed */
    if (cinfo->restart_interval)
      if (entropy->restarts_to_go == 0)
        emit_restart_e(entropy, entropy->next_restart_num);
  
    /* Encode the MCU data blocks */
    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      block = MCU_data[blkn];
      ci = cinfo->MCU_membership[blkn];
      compptr = cinfo->cur_comp_info[ci];
  
      /* Compute the DC value after the required point transform by Al.
       * This is simply an arithmetic right shift.
       */
      temp2 = IRIGHT_SHIFT((int) ((*block)[0]), Al);
  
      /* DC differences are figured on the point-transformed values. */
      temp = temp2 - entropy->saved.last_dc_val[ci];
      entropy->saved.last_dc_val[ci] = temp2;
  
      /* Encode the DC coefficient difference per section G.1.2.1 */
      temp2 = temp;
      if (temp < 0) {
        temp = -temp;		/* temp is abs value of input */
        /* For a negative input, want temp2 = bitwise complement of abs(input) */
        /* This code assumes we are on a two's complement machine */
        temp2--;
      }
      
      /* Find the number of bits needed for the magnitude of the coefficient */
      nbits = 0;
      while (temp) {
        nbits++;
        temp >>= 1;
      }
      /* Check for out-of-range coefficient values.
       * Since we're encoding a difference, the range limit is twice as much.
       */
      if (nbits > MAX_COEF_BITS+1)
        ERREXIT(cinfo, JERR_BAD_DCT_COEF);
      
      /* Count/emit the Huffman-coded symbol for the number of bits */
      emit_dc_symbol(entropy, compptr->dc_tbl_no, nbits);
      
      /* Emit that number of bits of the value, if positive, */
      /* or the complement of its magnitude, if negative. */
      if (nbits)			/* emit_bits rejects calls with size 0 */
        emit_bits_e(entropy, (unsigned int) temp2, nbits);
    }
  
    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
  
    /* Update restart-interval state too */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0) {
        entropy->restarts_to_go = cinfo->restart_interval;
        entropy->next_restart_num++;
        entropy->next_restart_num &= 7;
      }
      entropy->restarts_to_go--;
    }
  
    return TRUE;
  }
  
  
  /*
   * MCU encoding for AC initial scan (either spectral selection,
   * or first pass of successive approximation).
   */
  
  METHODDEF(BoolLean)
  encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    register int temp, temp2;
    register int nbits;
    register int r, k;
    int Se, Al;
    const int * natural_order;
    JBLOCKROW block;
  
    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
  
    /* Emit restart marker if needed */
    if (cinfo->restart_interval)
      if (entropy->restarts_to_go == 0)
        emit_restart_e(entropy, entropy->next_restart_num);
  
    Se = cinfo->Se;
    Al = cinfo->Al;
    natural_order = cinfo->natural_order;
  
    /* Encode the MCU data block */
    block = MCU_data[0];
  
    /* Encode the AC coefficients per section G.1.2.2, fig. G.3 */
    
    r = 0;			/* r = run length of zeros */
     
    for (k = cinfo->Ss; k <= Se; k++) {
      if ((temp = (*block)[natural_order[k]]) == 0) {
        r++;
        continue;
      }
      /* We must apply the point transform by Al.  For AC coefficients this
       * is an integer division with rounding towards 0.  To do this portably
       * in C, we shift after obtaining the absolute value; so the code is
       * interwoven with finding the abs value (temp) and output bits (temp2).
       */
      if (temp < 0) {
        temp = -temp;		/* temp is abs value of input */
        temp >>= Al;		/* apply the point transform */
        /* For a negative coef, want temp2 = bitwise complement of abs(coef) */
        temp2 = ~temp;
      } else {
        temp >>= Al;		/* apply the point transform */
        temp2 = temp;
      }
      /* Watch out for case that nonzero coef is zero after point transform */
      if (temp == 0) {
        r++;
        continue;
      }
  
      /* Emit any pending EOBRUN */
      if (entropy->EOBRUN > 0)
        emit_eobrun(entropy);
      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
      while (r > 15) {
        emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);
        r -= 16;
      }
  
      /* Find the number of bits needed for the magnitude of the coefficient */
      nbits = 1;			/* there must be at least one 1 bit */
      while ((temp >>= 1))
        nbits++;
      /* Check for out-of-range coefficient values */
      if (nbits > MAX_COEF_BITS)
        ERREXIT(cinfo, JERR_BAD_DCT_COEF);
  
      /* Count/emit Huffman symbol for run length / number of bits */
      emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + nbits);
  
      /* Emit that number of bits of the value, if positive, */
      /* or the complement of its magnitude, if negative. */
      emit_bits_e(entropy, (unsigned int) temp2, nbits);
  
      r = 0;			/* reset zero run length */
    }
  
    if (r > 0) {			/* If there are trailing zeroes, */
      entropy->EOBRUN++;		/* count an EOB */
      if (entropy->EOBRUN == 0x7FFF)
        emit_eobrun(entropy);	/* force it out to avoid overflow */
    }
  
    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
  
    /* Update restart-interval state too */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0) {
        entropy->restarts_to_go = cinfo->restart_interval;
        entropy->next_restart_num++;
        entropy->next_restart_num &= 7;
      }
      entropy->restarts_to_go--;
    }
  
    return TRUE;
  }
  
  
  /*
   * MCU encoding for DC successive approximation refinement scan.
   * Note: we assume such scans can be multi-component, although the spec
   * is not very clear on the point.
   */
  
  METHODDEF(BoolLean)
  encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    register int temp;
    int blkn;
    int Al = cinfo->Al;
    JBLOCKROW block;
  
    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
  
    /* Emit restart marker if needed */
    if (cinfo->restart_interval)
      if (entropy->restarts_to_go == 0)
        emit_restart_e(entropy, entropy->next_restart_num);
  
    /* Encode the MCU data blocks */
    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      block = MCU_data[blkn];
  
      /* We simply emit the Al'th bit of the DC coefficient value. */
      temp = (*block)[0];
      emit_bits_e(entropy, (unsigned int) (temp >> Al), 1);
    }
  
    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
  
    /* Update restart-interval state too */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0) {
        entropy->restarts_to_go = cinfo->restart_interval;
        entropy->next_restart_num++;
        entropy->next_restart_num &= 7;
      }
      entropy->restarts_to_go--;
    }
  
    return TRUE;
  }
  
  
  /*
   * MCU encoding for AC successive approximation refinement scan.
   */
  
  METHODDEF(BoolLean)
  encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    register int temp;
    register int r, k;
    int EOB;
    char *BR_buffer;
    unsigned int BR;
    int Se, Al;
    const int * natural_order;
    JBLOCKROW block;
    int absvalues[DCTSIZE2];
  
    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
  
    /* Emit restart marker if needed */
    if (cinfo->restart_interval)
      if (entropy->restarts_to_go == 0)
        emit_restart_e(entropy, entropy->next_restart_num);
  
    Se = cinfo->Se;
    Al = cinfo->Al;
    natural_order = cinfo->natural_order;
  
    /* Encode the MCU data block */
    block = MCU_data[0];
  
    /* It is convenient to make a pre-pass to determine the transformed
     * coefficients' absolute values and the EOB position.
     */
    EOB = 0;
    for (k = cinfo->Ss; k <= Se; k++) {
      temp = (*block)[natural_order[k]];
      /* We must apply the point transform by Al.  For AC coefficients this
       * is an integer division with rounding towards 0.  To do this portably
       * in C, we shift after obtaining the absolute value.
       */
      if (temp < 0)
        temp = -temp;		/* temp is abs value of input */
      temp >>= Al;		/* apply the point transform */
      absvalues[k] = temp;	/* save abs value for main pass */
      if (temp == 1)
        EOB = k;			/* EOB = index of last newly-nonzero coef */
    }
  
    /* Encode the AC coefficients per section G.1.2.3, fig. G.7 */
    
    r = 0;			/* r = run length of zeros */
    BR = 0;			/* BR = count of buffered bits added now */
    BR_buffer = entropy->bit_buffer + entropy->BE; /* Append bits to buffer */
  
    for (k = cinfo->Ss; k <= Se; k++) {
      if ((temp = absvalues[k]) == 0) {
        r++;
        continue;
      }
  
      /* Emit any required ZRLs, but not if they can be folded into EOB */
      while (r > 15 && k <= EOB) {
        /* emit any pending EOBRUN and the BE correction bits */
        emit_eobrun(entropy);
        /* Emit ZRL */
        emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);
        r -= 16;
        /* Emit buffered correction bits that must be associated with ZRL */
        emit_buffered_bits(entropy, BR_buffer, BR);
        BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
        BR = 0;
      }
  
      /* If the coef was previously nonzero, it only needs a correction bit.
       * NOTE: a straight translation of the spec's figure G.7 would suggest
       * that we also need to test r > 15.  But if r > 15, we can only get here
       * if k > EOB, which implies that this coefficient is not 1.
       */
      if (temp > 1) {
        /* The correction bit is the next bit of the absolute value. */
        BR_buffer[BR++] = (char) (temp & 1);
        continue;
      }
  
      /* Emit any pending EOBRUN and the BE correction bits */
      emit_eobrun(entropy);
  
      /* Count/emit Huffman symbol for run length / number of bits */
      emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + 1);
  
      /* Emit output bit for newly-nonzero coef */
      temp = ((*block)[natural_order[k]] < 0) ? 0 : 1;
      emit_bits_e(entropy, (unsigned int) temp, 1);
  
      /* Emit buffered correction bits that must be associated with this code */
      emit_buffered_bits(entropy, BR_buffer, BR);
      BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
      BR = 0;
      r = 0;			/* reset zero run length */
    }
  
    if (r > 0 || BR > 0) {	/* If there are trailing zeroes, */
      entropy->EOBRUN++;		/* count an EOB */
      entropy->BE += BR;		/* concat my correction bits to older ones */
      /* We force out the EOB if we risk either:
       * 1. overflow of the EOB counter;
       * 2. overflow of the correction bit buffer during the next MCU.
       */
      if (entropy->EOBRUN == 0x7FFF || entropy->BE > (MAX_CORR_BITS-DCTSIZE2+1))
        emit_eobrun(entropy);
    }
  
    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
  
    /* Update restart-interval state too */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0) {
        entropy->restarts_to_go = cinfo->restart_interval;
        entropy->next_restart_num++;
        entropy->next_restart_num &= 7;
      }
      entropy->restarts_to_go--;
    }
  
    return TRUE;
  }
  
  
  /* Encode a single block's worth of coefficients */
  
  LOCAL(BoolLean)
  encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
  		  c_derived_tbl *dctbl, c_derived_tbl *actbl)
  {
    register int temp, temp2;
    register int nbits;
    register int k, r, i;
    int Se = state->cinfo->lim_Se;
    const int * natural_order = state->cinfo->natural_order;
  
    /* Encode the DC coefficient difference per section F.1.2.1 */
  
    temp = temp2 = block[0] - last_dc_val;
  
    if (temp < 0) {
      temp = -temp;		/* temp is abs value of input */
      /* For a negative input, want temp2 = bitwise complement of abs(input) */
      /* This code assumes we are on a two's complement machine */
      temp2--;
    }
  
    /* Find the number of bits needed for the magnitude of the coefficient */
    nbits = 0;
    while (temp) {
      nbits++;
      temp >>= 1;
    }
    /* Check for out-of-range coefficient values.
     * Since we're encoding a difference, the range limit is twice as much.
     */
    if (nbits > MAX_COEF_BITS+1)
      ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
  
    /* Emit the Huffman-coded symbol for the number of bits */
    if (! emit_bits_s(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
      return FALSE;
  
    /* Emit that number of bits of the value, if positive, */
    /* or the complement of its magnitude, if negative. */
    if (nbits)			/* emit_bits rejects calls with size 0 */
      if (! emit_bits_s(state, (unsigned int) temp2, nbits))
        return FALSE;
  
    /* Encode the AC coefficients per section F.1.2.2 */
  
    r = 0;			/* r = run length of zeros */
  
    for (k = 1; k <= Se; k++) {
      if ((temp = block[natural_order[k]]) == 0) {
        r++;
      } else {
        /* if run length > 15, must emit special run-length-16 codes (0xF0) */
        while (r > 15) {
  	if (! emit_bits_s(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
  	  return FALSE;
  	r -= 16;
        }
  
        temp2 = temp;
        if (temp < 0) {
  	temp = -temp;		/* temp is abs value of input */
  	/* This code assumes we are on a two's complement machine */
  	temp2--;
        }
  
        /* Find the number of bits needed for the magnitude of the coefficient */
        nbits = 1;		/* there must be at least one 1 bit */
        while ((temp >>= 1))
  	nbits++;
        /* Check for out-of-range coefficient values */
        if (nbits > MAX_COEF_BITS)
  	ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
  
        /* Emit Huffman symbol for run length / number of bits */
        i = (r << 4) + nbits;
        if (! emit_bits_s(state, actbl->ehufco[i], actbl->ehufsi[i]))
  	return FALSE;
  
        /* Emit that number of bits of the value, if positive, */
        /* or the complement of its magnitude, if negative. */
        if (! emit_bits_s(state, (unsigned int) temp2, nbits))
  	return FALSE;
  
        r = 0;
      }
    }
  
    /* If the last coef(s) were zero, emit an end-of-block code */
    if (r > 0)
      if (! emit_bits_s(state, actbl->ehufco[0], actbl->ehufsi[0]))
        return FALSE;
  
    return TRUE;
  }
  
  
  /*
   * Encode and output one MCU's worth of Huffman-compressed coefficients.
   */
  
  METHODDEF(BoolLean)
  encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    working_state state;
    int blkn, ci;
    jpeg_component_info * compptr;
  
    /* Load up working state */
    state.next_output_byte = cinfo->dest->next_output_byte;
    state.free_in_buffer = cinfo->dest->free_in_buffer;
    ASSIGN_STATE(state.cur, entropy->saved);
    state.cinfo = cinfo;
  
    /* Emit restart marker if needed */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0)
        if (! emit_restart_s(&state, entropy->next_restart_num))
  	return FALSE;
    }
  
    /* Encode the MCU data blocks */
    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      ci = cinfo->MCU_membership[blkn];
      compptr = cinfo->cur_comp_info[ci];
      if (! encode_one_block(&state,
  			   MCU_data[blkn][0], state.cur.last_dc_val[ci],
  			   entropy->dc_derived_tbls[compptr->dc_tbl_no],
  			   entropy->ac_derived_tbls[compptr->ac_tbl_no]))
        return FALSE;
      /* Update last_dc_val */
      state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
    }
  
    /* Completed MCU, so update state */
    cinfo->dest->next_output_byte = state.next_output_byte;
    cinfo->dest->free_in_buffer = state.free_in_buffer;
    ASSIGN_STATE(entropy->saved, state.cur);
  
    /* Update restart-interval state too */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0) {
        entropy->restarts_to_go = cinfo->restart_interval;
        entropy->next_restart_num++;
        entropy->next_restart_num &= 7;
      }
      entropy->restarts_to_go--;
    }
  
    return TRUE;
  }
  
  
  /*
   * Finish up at the end of a Huffman-compressed scan.
   */
  
  METHODDEF(void)
  finish_pass_huff (j_compress_ptr cinfo)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    working_state state;
  
    if (cinfo->progressive_mode) {
      entropy->next_output_byte = cinfo->dest->next_output_byte;
      entropy->free_in_buffer = cinfo->dest->free_in_buffer;
  
      /* Flush out any buffered data */
      emit_eobrun(entropy);
      flush_bits_e(entropy);
  
      cinfo->dest->next_output_byte = entropy->next_output_byte;
      cinfo->dest->free_in_buffer = entropy->free_in_buffer;
    } else {
      /* Load up working state ... flush_bits needs it */
      state.next_output_byte = cinfo->dest->next_output_byte;
      state.free_in_buffer = cinfo->dest->free_in_buffer;
      ASSIGN_STATE(state.cur, entropy->saved);
      state.cinfo = cinfo;
  
      /* Flush out the last data */
      if (! flush_bits_s(&state))
        ERREXIT(cinfo, JERR_CANT_SUSPEND);
  
      /* Update state */
      cinfo->dest->next_output_byte = state.next_output_byte;
      cinfo->dest->free_in_buffer = state.free_in_buffer;
      ASSIGN_STATE(entropy->saved, state.cur);
    }
  }
  
  
  /*
   * Huffman coding optimization.
   *
   * We first scan the supplied data and count the number of uses of each symbol
   * that is to be Huffman-coded. (This process MUST agree with the code above.)
   * Then we build a Huffman coding tree for the observed counts.
   * Symbols which are not needed at all for the particular image are not
   * assigned any code, which saves space in the DHT marker as well as in
   * the compressed data.
   */
  
  
  /* Process a single block's worth of coefficients */
  
  LOCAL(void)
  htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
  		 long dc_counts[], long ac_counts[])
  {
    register int temp;
    register int nbits;
    register int k, r;
    int Se = cinfo->lim_Se;
    const int * natural_order = cinfo->natural_order;
    
    /* Encode the DC coefficient difference per section F.1.2.1 */
    
    temp = block[0] - last_dc_val;
    if (temp < 0)
      temp = -temp;
    
    /* Find the number of bits needed for the magnitude of the coefficient */
    nbits = 0;
    while (temp) {
      nbits++;
      temp >>= 1;
    }
    /* Check for out-of-range coefficient values.
     * Since we're encoding a difference, the range limit is twice as much.
     */
    if (nbits > MAX_COEF_BITS+1)
      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
  
    /* Count the Huffman symbol for the number of bits */
    dc_counts[nbits]++;
    
    /* Encode the AC coefficients per section F.1.2.2 */
    
    r = 0;			/* r = run length of zeros */
    
    for (k = 1; k <= Se; k++) {
      if ((temp = block[natural_order[k]]) == 0) {
        r++;
      } else {
        /* if run length > 15, must emit special run-length-16 codes (0xF0) */
        while (r > 15) {
  	ac_counts[0xF0]++;
  	r -= 16;
        }
        
        /* Find the number of bits needed for the magnitude of the coefficient */
        if (temp < 0)
  	temp = -temp;
        
        /* Find the number of bits needed for the magnitude of the coefficient */
        nbits = 1;		/* there must be at least one 1 bit */
        while ((temp >>= 1))
  	nbits++;
        /* Check for out-of-range coefficient values */
        if (nbits > MAX_COEF_BITS)
  	ERREXIT(cinfo, JERR_BAD_DCT_COEF);
        
        /* Count Huffman symbol for run length / number of bits */
        ac_counts[(r << 4) + nbits]++;
        
        r = 0;
      }
    }
  
    /* If the last coef(s) were zero, emit an end-of-block code */
    if (r > 0)
      ac_counts[0]++;
  }
  
  
  /*
   * Trial-encode one MCU's worth of Huffman-compressed coefficients.
   * No data is actually output, so no suspension return is possible.
   */
  
  METHODDEF(BoolLean)
  encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    int blkn, ci;
    jpeg_component_info * compptr;
  
    /* Take care of restart intervals if needed */
    if (cinfo->restart_interval) {
      if (entropy->restarts_to_go == 0) {
        /* Re-initialize DC predictions to 0 */
        for (ci = 0; ci < cinfo->comps_in_scan; ci++)
  	entropy->saved.last_dc_val[ci] = 0;
        /* Update restart state */
        entropy->restarts_to_go = cinfo->restart_interval;
      }
      entropy->restarts_to_go--;
    }
  
    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      ci = cinfo->MCU_membership[blkn];
      compptr = cinfo->cur_comp_info[ci];
      htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
  		    entropy->dc_count_ptrs[compptr->dc_tbl_no],
  		    entropy->ac_count_ptrs[compptr->ac_tbl_no]);
      entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
    }
  
    return TRUE;
  }
  
  
  /*
   * Generate the best Huffman code table for the given counts, fill htbl.
   *
   * The JPEG standard requires that no symbol be assigned a codeword of all
   * one bits (so that padding bits added at the end of a compressed segment
   * can't look like a valid code).  Because of the canonical ordering of
   * codewords, this just means that there must be an unused slot in the
   * longest codeword length category.  Section K.2 of the JPEG spec suggests
   * reserving such a slot by pretending that symbol 256 is a valid symbol
   * with count 1.  In theory that's not optimal; giving it count zero but
   * including it in the symbol set anyway should give a better Huffman code.
   * But the theoretically better code actually seems to come out worse in
   * practice, because it produces more all-ones bytes (which incur stuffed
   * zero bytes in the final file).  In any case the difference is tiny.
   *
   * The JPEG standard requires Huffman codes to be no more than 16 bits long.
   * If some symbols have a very small but nonzero probability, the Huffman tree
   * must be adjusted to meet the code length restriction.  We currently use
   * the adjustment method suggested in JPEG section K.2.  This method is *not*
   * optimal; it may not choose the best possible limited-length code.  But
   * typically only very-low-frequency symbols will be given less-than-optimal
   * lengths, so the code is almost optimal.  Experimental comparisons against
   * an optimal limited-length-code algorithm indicate that the difference is
   * microscopic --- usually less than a hundredth of a percent of total size.
   * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
   */
  
  LOCAL(void)
  jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
  {
  #define MAX_CLEN 32		/* assumed maximum initial code length */
    UINT8 bits[MAX_CLEN+1];	/* bits[k] = # of symbols with code length k */
    int codesize[257];		/* codesize[k] = code length of symbol k */
    int others[257];		/* next symbol in current branch of tree */
    int c1, c2;
    int p, i, j;
    long v;
  
    /* This algorithm is explained in section K.2 of the JPEG standard */
  
    MEMZERO(bits, SIZEOF(bits));
    MEMZERO(codesize, SIZEOF(codesize));
    for (i = 0; i < 257; i++)
      others[i] = -1;		/* init links to empty */
    
    freq[256] = 1;		/* make sure 256 has a nonzero count */
    /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
     * that no real symbol is given code-value of all ones, because 256
     * will be placed last in the largest codeword category.
     */
  
    /* Huffman's basic algorithm to assign optimal code lengths to symbols */
  
    for (;;) {
      /* Find the smallest nonzero frequency, set c1 = its symbol */
      /* In case of ties, take the larger symbol number */
      c1 = -1;
      v = 1000000000L;
      for (i = 0; i <= 256; i++) {
        if (freq[i] && freq[i] <= v) {
  	v = freq[i];
  	c1 = i;
        }
      }
  
      /* Find the next smallest nonzero frequency, set c2 = its symbol */
      /* In case of ties, take the larger symbol number */
      c2 = -1;
      v = 1000000000L;
      for (i = 0; i <= 256; i++) {
        if (freq[i] && freq[i] <= v && i != c1) {
  	v = freq[i];
  	c2 = i;
        }
      }
  
      /* Done if we've merged everything into one frequency */
      if (c2 < 0)
        break;
      
      /* Else merge the two counts/trees */
      freq[c1] += freq[c2];
      freq[c2] = 0;
  
      /* Increment the codesize of everything in c1's tree branch */
      codesize[c1]++;
      while (others[c1] >= 0) {
        c1 = others[c1];
        codesize[c1]++;
      }
      
      others[c1] = c2;		/* chain c2 onto c1's tree branch */
      
      /* Increment the codesize of everything in c2's tree branch */
      codesize[c2]++;
      while (others[c2] >= 0) {
        c2 = others[c2];
        codesize[c2]++;
      }
    }
  
    /* Now count the number of symbols of each code length */
    for (i = 0; i <= 256; i++) {
      if (codesize[i]) {
        /* The JPEG standard seems to think that this can't happen, */
        /* but I'm paranoid... */
        if (codesize[i] > MAX_CLEN)
  	ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
  
        bits[codesize[i]]++;
      }
    }
  
    /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
     * Huffman procedure assigned any such lengths, we must adjust the coding.
     * Here is what the JPEG spec says about how this next bit works:
     * Since symbols are paired for the longest Huffman code, the symbols are
     * removed from this length category two at a time.  The prefix for the pair
     * (which is one bit shorter) is allocated to one of the pair; then,
     * skipping the BITS entry for that prefix length, a code word from the next
     * shortest nonzero BITS entry is converted into a prefix for two code words
     * one bit longer.
     */
    
    for (i = MAX_CLEN; i > 16; i--) {
      while (bits[i] > 0) {
        j = i - 2;		/* find length of new prefix to be used */
        while (bits[j] == 0)
  	j--;
        
        bits[i] -= 2;		/* remove two symbols */
        bits[i-1]++;		/* one goes in this length */
        bits[j+1] += 2;		/* two new symbols in this length */
        bits[j]--;		/* symbol of this length is now a prefix */
      }
    }
  
    /* Remove the count for the pseudo-symbol 256 from the largest codelength */
    while (bits[i] == 0)		/* find largest codelength still in use */
      i--;
    bits[i]--;
    
    /* Return final symbol counts (only for lengths 0..16) */
    MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));
    
    /* Return a list of the symbols sorted by code length */
    /* It's not real clear to me why we don't need to consider the codelength
     * changes made above, but the JPEG spec seems to think this works.
     */
    p = 0;
    for (i = 1; i <= MAX_CLEN; i++) {
      for (j = 0; j <= 255; j++) {
        if (codesize[j] == i) {
  	htbl->huffval[p] = (UINT8) j;
  	p++;
        }
      }
    }
  
    /* Set sent_table FALSE so updated table will be written to JPEG file. */
    htbl->sent_table = FALSE;
  }
  
  
  /*
   * Finish up a statistics-gathering pass and create the new Huffman tables.
   */
  
  METHODDEF(void)
  finish_pass_gather (j_compress_ptr cinfo)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    int ci, tbl;
    jpeg_component_info * compptr;
    JHUFF_TBL **htblptr;
    BoolLean did_dc[NUM_HUFF_TBLS];
    BoolLean did_ac[NUM_HUFF_TBLS];
  
    /* It's important not to apply jpeg_gen_optimal_table more than once
     * per table, because it clobbers the input frequency counts!
     */
    if (cinfo->progressive_mode)
      /* Flush out buffered data (all we care about is counting the EOB symbol) */
      emit_eobrun(entropy);
  
    MEMZERO(did_dc, SIZEOF(did_dc));
    MEMZERO(did_ac, SIZEOF(did_ac));
  
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      /* DC needs no table for refinement scan */
      if (cinfo->Ss == 0 && cinfo->Ah == 0) {
        tbl = compptr->dc_tbl_no;
        if (! did_dc[tbl]) {
  	htblptr = & cinfo->dc_huff_tbl_ptrs[tbl];
  	if (*htblptr == NULL)
  	  *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
  	jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[tbl]);
  	did_dc[tbl] = TRUE;
        }
      }
      /* AC needs no table when not present */
      if (cinfo->Se) {
        tbl = compptr->ac_tbl_no;
        if (! did_ac[tbl]) {
  	htblptr = & cinfo->ac_huff_tbl_ptrs[tbl];
  	if (*htblptr == NULL)
  	  *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
  	jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[tbl]);
  	did_ac[tbl] = TRUE;
        }
      }
    }
  }
  
  
  /*
   * Initialize for a Huffman-compressed scan.
   * If gather_statistics is TRUE, we do not output anything during the scan,
   * just count the Huffman symbols used and generate Huffman code tables.
   */
  
  METHODDEF(void)
  start_pass_huff (j_compress_ptr cinfo, BoolLean gather_statistics)
  {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    int ci, tbl;
    jpeg_component_info * compptr;
  
    if (gather_statistics)
      entropy->pub.finish_pass = finish_pass_gather;
    else
      entropy->pub.finish_pass = finish_pass_huff;
  
    if (cinfo->progressive_mode) {
      entropy->cinfo = cinfo;
      entropy->gather_statistics = gather_statistics;
  
      /* We assume jcmaster.c already validated the scan parameters. */
  
      /* Select execution routine */
      if (cinfo->Ah == 0) {
        if (cinfo->Ss == 0)
  	entropy->pub.encode_mcu = encode_mcu_DC_first;
        else
  	entropy->pub.encode_mcu = encode_mcu_AC_first;
      } else {
        if (cinfo->Ss == 0)
  	entropy->pub.encode_mcu = encode_mcu_DC_refine;
        else {
  	entropy->pub.encode_mcu = encode_mcu_AC_refine;
  	/* AC refinement needs a correction bit buffer */
  	if (entropy->bit_buffer == NULL)
  	  entropy->bit_buffer = (char *)
  	    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  					MAX_CORR_BITS * SIZEOF(char));
        }
      }
  
      /* Initialize AC stuff */
      entropy->ac_tbl_no = cinfo->cur_comp_info[0]->ac_tbl_no;
      entropy->EOBRUN = 0;
      entropy->BE = 0;
    } else {
      if (gather_statistics)
        entropy->pub.encode_mcu = encode_mcu_gather;
      else
        entropy->pub.encode_mcu = encode_mcu_huff;
    }
  
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      /* DC needs no table for refinement scan */
      if (cinfo->Ss == 0 && cinfo->Ah == 0) {
        tbl = compptr->dc_tbl_no;
        if (gather_statistics) {
  	/* Check for invalid table index */
  	/* (make_c_derived_tbl does this in the other path) */
  	if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
  	  ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
  	/* Allocate and zero the statistics tables */
  	/* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
  	if (entropy->dc_count_ptrs[tbl] == NULL)
  	  entropy->dc_count_ptrs[tbl] = (long *)
  	    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  					257 * SIZEOF(long));
  	MEMZERO(entropy->dc_count_ptrs[tbl], 257 * SIZEOF(long));
        } else {
  	/* Compute derived values for Huffman tables */
  	/* We may do this more than once for a table, but it's not expensive */
  	jpeg_make_c_derived_tbl(cinfo, TRUE, tbl,
  				& entropy->dc_derived_tbls[tbl]);
        }
        /* Initialize DC predictions to 0 */
        entropy->saved.last_dc_val[ci] = 0;
      }
      /* AC needs no table when not present */
      if (cinfo->Se) {
        tbl = compptr->ac_tbl_no;
        if (gather_statistics) {
  	if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
  	  ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
  	if (entropy->ac_count_ptrs[tbl] == NULL)
  	  entropy->ac_count_ptrs[tbl] = (long *)
  	    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  					257 * SIZEOF(long));
  	MEMZERO(entropy->ac_count_ptrs[tbl], 257 * SIZEOF(long));
        } else {
  	jpeg_make_c_derived_tbl(cinfo, FALSE, tbl,
  				& entropy->ac_derived_tbls[tbl]);
        }
      }
    }
  
    /* Initialize bit buffer to empty */
    entropy->saved.put_buffer = 0;
    entropy->saved.put_bits = 0;
  
    /* Initialize restart stuff */
    entropy->restarts_to_go = cinfo->restart_interval;
    entropy->next_restart_num = 0;
  }
  
  
  /*
   * Module initialization routine for Huffman entropy encoding.
   */
  
  GLOBAL(void)
  jinit_huff_encoder (j_compress_ptr cinfo)
  {
    huff_entropy_ptr entropy;
    int i;
  
    entropy = (huff_entropy_ptr)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				SIZEOF(huff_entropy_encoder));
    cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
    entropy->pub.start_pass = start_pass_huff;
  
    /* Mark tables unallocated */
    for (i = 0; i < NUM_HUFF_TBLS; i++) {
      entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
      entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
    }
  
    if (cinfo->progressive_mode)
      entropy->bit_buffer = NULL;	/* needed only in AC refinement scan */
  }
  